the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Jan 2026
Glacial-interglacial shifts in dominant climate forcing over the last 33 ka in the northern South China Sea
Abstract. The northern South China Sea is a critical region for understanding East Asian Monsoon dynamics. However, integrated, multi-proxy records elucidating long-term climatic and vegetation changes in this region remain fragmented, with a notable scarcity of coherent land-ocean interaction data during the Last Glacial Maximum (LGM). This gap has impeded progress in elucidating the mechanisms underpinning monsoon variability and in rigorously evaluating the performance of palaeoclimate models. To address this, we conducted a multi-proxy analysis combining palynological, organic- and inorganic-geochemical methods on a marine sediment core from the northern South China Sea to reconstruct environmental and oceanic dynamics at millennial-scale resolution that spans the last 33 ka. Our results reveal a clear contrast between glacial and interglacial conditions and drivers: the glacial period was characterized by higher sedimentation rates, elevated marine primary productivity, cooler climate, lower humidity and herb-dominated vegetation associated with enhanced fire activity in the adjacent terrestrial ecosystems. Deglaciation was characterized by pronounced warming and reduced productivity, together with increased moisture availability, a shift toward pine-dominated vegetation, minimal fire activity, and reduced fluvial input as the coastline retreated. The overall findings highlight a fundamental transition in climatic controls, from a regime dominated by sea level forcing during the glacial period to one increasingly governed by tropical ocean-atmosphere interactions initiated by early ocean warming during the interglacial.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-6415', Anonymous Referee #1, 31 Jan 2026
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RC2: 'Comment on egusphere-2025-6415', Anonymous Referee #2, 02 Feb 2026
Zhao et al.’s manuscript presents a multi-proxy study of a core from the South China Sea using a wide range of tracers, including microfossil (dinocyst, microcharcoal, pollen) and bio-geochemical proxies (TOC, TN, XRF elemental data, isotopic analysis from planktonic foraminifera, and Mg/Ca-SST). I do not question the quality of the data or the multi-proxy approach of the study. Indeed, the authors have made a remarkable effort to integrate the various proxy data in order to propose a coherent environmental reconstruction. However, this work aims to propose a conceptual framework to explain the observed variations in the different tracers and it provides little discussion and advancement in our understanding of the climate variability affecting oceanographic and atmospheric circulations in the East Asian tropics/subtropics.
Furthermore, this article has some gaps and weaknesses. In particular, it does not consider the millennial climate variability affecting deglaciation (e.g., the interval associated with the LGM is much larger than the LGM itself and includes the Heinrich Stadial 1), and the zonation and representation of pollen data is questionable.
In my opinion, there is not enough in-depth paleoclimatic discussion. Submitting this work to a journal with a slightly different scope would be a favorable option.
Detailed comments:
L.79-83: In the section (2.1 Atmospheric circulation and climate): Please, add information on the mean temperature and precipitation during the summer and winter monsoon season on the adjacent landmasses, as well as on the latitudinal and seasonal temperature gradients. This information is required to relate climate to vegetation distribution.
Please also provide information on the main taxa that are included within the dominant vegetation types of the study area. This would greatly help the reader to related the main pollen taxa to the vegetation
l.156 : Primostar?
L.177: Was the CANOCO software used only for dinoyst data or for both pollen and dinocyst data?
L.182: Was the cluster analysis performed on both pollen and dinocyst data together, or were separate analyses conducted for each dataset? This is unclear here. The cluster analysis should not include both proxy datasets because they give different information.
L.212: Should be “stable carbon δ13CVPDB”
L.229: Variable pollen concentration may also be attributable to changes in pollen supply and sea level changes rather than pollen preservation only. Is there any evidence of variations in pollen preservation, for instance intervals with increasing corroded pollen?
L.238: Please, explain what the shading represents. If it refers to uncertainties in pollen percentages, how were these calculated?
I also recommend presenting the pollen data, at least in a supplementary figure, with pollen percentages calculated based on a pollen sum excluding Pinus. Pinus is always overrepresented in marine sediments; excluding pollen from the main allows better evaluation of changes in other taxa, which are likely underrepresented when Pinus become dominant. In addition, if Pinus pollen originates from a far-distant vegetation and is mainly supplied to the site by long-distance winter monsoon wind transport, it is even more useful to present a diagram with percentages based on a pollen sum excluding Pinus.
In the supplementary material, more detailed percentage diagram and a diagram showing pollen taxa concentrations are also needed. The number of taxa shown in the current percentage diagram is too restricted to discuss the pollen source vegetation adequately.
L.327: Cyperaceae does not exclusively indicate wet environments; it can develop with Poaceae in dry grasslands or semi-arid steppes. Poaceae, Cyperaceae and semi-arid taxa such as Artemisia often develop together in subtropical/tropoical dry glacial environments or in modern drylands such as in the Middle East.
Pollen diagram zonation should be done for pollen and dinocyst separately. It is not reliable to assume that dinocyst (and thus sea surface changes) will occur consistently or synchronously with pollen changes These records should be compared, not amalgamated.
The authors define pollen zone 2 as the LGM but this zone ends at 15.6 ka, therefore largely later than the LGM. It includes the HS-1. I wonder whether CONISS applied only to pollen data and to percentages excluding Pinus would produce a similar zonation. Is millennial-scale variability during the deglaciation detected in pollen or dinocyst data?
L.387: Can the tree/herb ratio low values only be explained by the expansion of vegetation on the exposed shelf due to lower sea-level? Higher pollen and charcoal concentrations may also be due to a more open vegetation and a lesser silico-clastic input (as shown by lower sedimentation rate). Why is the expansion of open vegetation in the river catchments of the study area not considered? May the microcharcoal and pollen data be also interpreted in terms of variability in fire regime depending on the vegetation type and structure and climate conditions?
Citation: https://doi.org/10.5194/egusphere-2025-6415-RC2
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This manuscript employs multiple proxies—including pollen, dinoflagellate cysts, total organic carbon (TOC), total nitrogen (TN), foraminiferal Mg/Ca ratios, and XRF elemental analysis—to reconstruct environmental changes from a marine core in the northern South China Sea (SCS covering the Marine Isotope Stages 1-3. To date, numerous palynological and paleoceanographic studies from the northern SCS have already documented epicontinental vegetation dynamics and oceanographic variability since the last glaciation, along with their driving mechanisms, as exemplified by the classic work of Wang et al. (1999), East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea (Marine Geology). In comparison with these previous studies, however, this manuscript does not appear to offer clear new insights or conceptual advances. In addition, the discussion focuses predominantly on climatic responses (e.g., vegetation and SST changes), while the underlying climate forcing mechanisms are only weakly addressed. I therefore recommend a major revision to substantially strengthen the manuscript’s novelty and interpretative depth.
The pollen analysis does not present fundamentally new evidence regarding epicontinental vegetation changes. The most pronounced shift in pollen assemblages appears to be primarily controlled by changes in pollen source areas, from the exposed continental shelf during sea-level lowstands to inland regions during highstands. The authors need to provide more robust evidence to clarify the relationship between vegetation changes and climate forcing, rather than source-area effects alone. Moreover, lines 341–346 interpret Pinus pollen as an indicator of a strengthened winter monsoon or a cold–humid climate. If this interpretation is valid, how do the authors explain the substantially higher abundance of Pinus pollen during the Holocene compared with the Last Glacial Maximum?
Dinoflagellate cysts are a valuable proxy for reconstructing oceanographic conditions and fluvial influences, and they offer an important opportunity for synchronous land–ocean comparisons. I suggest that the manuscript should place greater emphasis on integrating dinoflagellate cyst data with other paleoceanographic proxies, such as biomarkers and foraminiferal records, in order to better distinguish between climate forcing and the oceanographic responses to that forcing.